Explanation of Optical Terms
made of a plastic resin material sometimes known as CR 39.
lenses.. Tougher than
traditional plastic lenses made of a polycarbonate material ,often used
in rimless spectacles, less likely to break. Used in Safety eyewear.
index Lenses… Plastic lenses
made of a denser resin enabling the lenses to be thinner and lighter
than traditional plastic lenses. There are differing degrees shown by
there index number, ie A standard lens has a index number of 1.52. Hi
index lenses start from 1.6 1.67
lenses… Lenses which incorporate the distance and reading prescriptions in one
lens. The top part of the lens is for distance vision the lower part for
reading vision. There is a dividing line between the two. There are many
different types of bifocals with different sizes and shapes of reading
Lenses…Lenses which gradually change power as you look down the lens from
distance to reading. Commonly known as Varifocal lenses. There are many
different lenses such as Varilux ..Progressive…Graduate.. Impressions.
Each manufacture having their own